org.apache.commons.configuration2.event

Class BaseEventSource

java.lang.Object

org.apache.commons.configuration2.event.BaseEventSource

All Implemented Interfaces:

EventSource

Direct Known Subclasses:

AbstractConfiguration

public class BaseEventSource
extends Object
implements EventSource

A base class for objects that can generate configuration events.

This class implements functionality for managing a set of event listeners that can be notified when an event occurs. It can be extended by configuration classes that support the event mechanism. In this case these classes only need to call the fireEvent() method when an event is to be delivered to the registered listeners.

Adding and removing event listeners can happen concurrently to manipulations on a configuration that cause events. The operations are synchronized.

With the detailEvents property the number of detail events can be controlled. Some methods in configuration classes are implemented in a way that they call other methods that can generate their own events. One example is the setProperty() method that can be implemented as a combination of clearProperty() and addProperty(). With detailEvents set to true, all involved methods will generate events (i.e. listeners will receive property set events, property clear events, and property add events). If this mode is turned off (which is the default), detail events are suppressed, so only property set events will be received. Note that the number of received detail events may differ for different configuration implementations. BaseHierarchicalConfiguration for instance has a custom implementation of setProperty(), which does not generate any detail events.

In addition to "normal" events, error events are supported. Such events signal an internal problem that occurred during access of properties. They are handled via the regular EventListener interface, but there are special event types defined by ConfigurationErrorEvent. The fireError() method can be used by derived classes to send notifications about errors to registered observers.

Since:

1.3

Constructor Summary

Constructors

Constructor and Description
BaseEventSource() Creates a new instance of BaseEventSource.

Method Summary

Modifier and Type	Method and Description
<T extends Event> void	addEventListener(EventType<T> eventType, EventListener<? super T> listener) Adds an event listener for the specified event type.
void	clearErrorListeners() Removes all registered error listeners.
void	clearEventListeners() Removes all registered event listeners.
protected Object	clone() Overrides the clone() method to correctly handle so far registered event listeners.
void	copyEventListeners(BaseEventSource source) Copies all event listener registrations maintained by this object to the specified BaseEventSource object.
protected ConfigurationErrorEvent	createErrorEvent(EventType<? extends ConfigurationErrorEvent> type, EventType<?> opType, String propName, Object propValue, Throwable ex) Creates a ConfigurationErrorEvent object based on the passed in parameters.
protected <T extends ConfigurationEvent> ConfigurationEvent	createEvent(EventType<T> type, String propName, Object propValue, boolean before) Creates a ConfigurationEvent object based on the passed in parameters.
<T extends ConfigurationErrorEvent> void	fireError(EventType<T> eventType, EventType<?> operationType, String propertyName, Object propertyValue, Throwable cause) Creates an error event object and delivers it to all registered error listeners of a matching type.
protected <T extends ConfigurationEvent> void	fireEvent(EventType<T> type, String propName, Object propValue, boolean before) Creates an event object and delivers it to all registered event listeners.
List<EventListenerRegistrationData<?>>	getEventListenerRegistrations() Returns a list with all EventListenerRegistrationData objects currently contained for this event source.
<T extends Event> Collection<EventListener<? super T>>	getEventListeners(EventType<T> eventType) Returns a collection with all event listeners of the specified event type that are currently registered at this object.
boolean	isDetailEvents() Returns a flag whether detail events are enabled.
<T extends Event> boolean	removeEventListener(EventType<T> eventType, EventListener<? super T> listener) Removes the event listener registration for the given event type and listener.
void	setDetailEvents(boolean enable) Determines whether detail events should be generated.

Methods inherited from class java.lang.Object

equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

BaseEventSource

public BaseEventSource()

Creates a new instance of BaseEventSource.

Method Detail

getEventListeners

public <T extends Event> Collection<EventListener<? super T>> getEventListeners(EventType<T> eventType)

Returns a collection with all event listeners of the specified event type that are currently registered at this object.

Type Parameters:

T - the event type

Parameters:

eventType - the event type object

Returns:

a collection with the event listeners of the specified event type (this collection is a snapshot of the currently registered listeners; it cannot be manipulated)

getEventListenerRegistrations

public List<EventListenerRegistrationData<?>> getEventListenerRegistrations()

Returns a list with all EventListenerRegistrationData objects currently contained for this event source. This method allows access to all registered event listeners, independent on their type.

Returns:

a list with information about all registered event listeners

isDetailEvents

public boolean isDetailEvents()

Returns a flag whether detail events are enabled.

Returns:

a flag if detail events are generated

setDetailEvents

public void setDetailEvents(boolean enable)

Determines whether detail events should be generated. If enabled, some methods can generate multiple update events. Note that this method records the number of calls, i.e. if for instance setDetailEvents(false) was called three times, you will have to invoke the method as often to enable the details.

Parameters:

enable - a flag if detail events should be enabled or disabled

addEventListener

public <T extends Event> void addEventListener(EventType<T> eventType,
                                               EventListener<? super T> listener)

Description copied from interface: EventSource

Adds an event listener for the specified event type. This listener is notified about events of this type and all its sub types.

Specified by:

addEventListener in interface EventSource

Type Parameters:

T - the type of events processed by this listener

Parameters:

eventType - the event type (must not be null)

listener - the listener to be registered (must not be null)

removeEventListener

public <T extends Event> boolean removeEventListener(EventType<T> eventType,
                                                     EventListener<? super T> listener)

Description copied from interface: EventSource

Removes the event listener registration for the given event type and listener. An event listener instance may be registered multiple times for different event types. Therefore, when removing a listener the event type of the registration in question has to be specified. The return value indicates whether a registration was removed. A value of false means that no such combination of event type and listener was found.

Specified by:

removeEventListener in interface EventSource

Type Parameters:

T - the type of events processed by this listener

Parameters:

eventType - the event type

listener - the event listener to be removed

Returns:

a flag whether a listener registration was removed

clearEventListeners

public void clearEventListeners()

Removes all registered event listeners.

clearErrorListeners

public void clearErrorListeners()

Removes all registered error listeners.

Since:

1.4

copyEventListeners

public void copyEventListeners(BaseEventSource source)

Copies all event listener registrations maintained by this object to the specified BaseEventSource object.

Parameters:

source - the target source for the copy operation (must not be null)

Throws:

IllegalArgumentException - if the target source is null

Since:

2.0

fireEvent

protected <T extends ConfigurationEvent> void fireEvent(EventType<T> type,
                                                        String propName,
                                                        Object propValue,
                                                        boolean before)

Creates an event object and delivers it to all registered event listeners. The method checks first if sending an event is allowed (making use of the detailEvents property), and if listeners are registered.

Type Parameters:

T - the type of the event to be fired

Parameters:

type - the event's type

propName - the name of the affected property (can be null)

propValue - the value of the affected property (can be null)

before - the before update flag

createEvent

protected <T extends ConfigurationEvent> ConfigurationEvent createEvent(EventType<T> type,
                                                                        String propName,
                                                                        Object propValue,
                                                                        boolean before)

Creates a ConfigurationEvent object based on the passed in parameters. This method is called by fireEvent() if it decides that an event needs to be generated.

Type Parameters:

T - the type of the event to be created

Parameters:

type - the event's type

propName - the name of the affected property (can be null)

propValue - the value of the affected property (can be null)

before - the before update flag

Returns:

the newly created event object

fireError

public <T extends ConfigurationErrorEvent> void fireError(EventType<T> eventType,
                                                          EventType<?> operationType,
                                                          String propertyName,
                                                          Object propertyValue,
                                                          Throwable cause)

Creates an error event object and delivers it to all registered error listeners of a matching type.

Type Parameters:

T - the event type

Parameters:

eventType - the event's type

operationType - the type of the failed operation

propertyName - the name of the affected property (can be null)

propertyValue - the value of the affected property (can be null)

cause - the Throwable object that caused this error event

createErrorEvent

protected ConfigurationErrorEvent createErrorEvent(EventType<? extends ConfigurationErrorEvent> type,
                                                   EventType<?> opType,
                                                   String propName,
                                                   Object propValue,
                                                   Throwable ex)

Creates a ConfigurationErrorEvent object based on the passed in parameters. This is called by fireError() if it decides that an event needs to be generated.

Parameters:

type - the event's type

opType - the operation type related to this error

propName - the name of the affected property (can be null)

propValue - the value of the affected property (can be null)

ex - the Throwable object that caused this error event

Returns:

the event object

clone

protected Object clone()
                throws CloneNotSupportedException

Overrides the clone() method to correctly handle so far registered event listeners. This implementation ensures that the clone will have empty event listener lists, i.e. the listeners registered at an BaseEventSource object will not be copied.

Overrides:

clone in class Object

Returns:

the cloned object

Throws:

CloneNotSupportedException - if cloning is not allowed

Since:

1.4